Moon Phase
Compute the moon's phase for any date: age in the synodic cycle, illuminated fraction, phase name, and the dates of the next new and full moons. Deterministic astronomy on the mean synodic month — the night-sky fact agents constantly misremember.
Worked examples
Tonight
GET /api/v1/geo-time/moon-phase?
Result: 80% illuminated — Waxing Gibbous (lunar day 10.5)
A full-moon date
GET /api/v1/geo-time/moon-phase?date=2026-01-03
Result: 100% illuminated — Full Moon (lunar day 14.4)
Apollo 11 landing
GET /api/v1/geo-time/moon-phase?date=1969-07-20
Result: 33% illuminated — Waxing Crescent (lunar day 5.8)
Machine API (x402)
$0.01 / callThis tool is also a JSON API for AI agents. Requests without payment receive 402 Payment Required plus instructions; agents pay USDC on Base via the x402 protocol — no accounts, no API keys.
GET /api/v1/geo-time/moon-phase? HTTP/1.1
Host: agentstoolshub.com
→ 402 (payment required, instructions in headers)
→ 200 (after X-PAYMENT header; JSON body below)
{
"tool": "geo-time/moon-phase",
"input": {},
"result": { "value": 80, "answer": "80% illuminated — Waxing Gibbous (lunar day 10.5)" }
}Agent docs: /llms.txt · OpenAPI spec · integration guide
About this tool
Exact moon phase from the mean synodic cycle: illuminated fraction, phase name, lunar day, and the next new/full moon dates. Same input, same answer — unlike the approximations models produce for 'what was the moon on X date', a classic factual trap.
Frequently asked questions
How accurate is it?
Within a few hours of true lunation (the mean synodic month ignores small perturbations). Phase name and illumination percent are reliable; eclipses are not modeled.
Which timezone is the date in?
UTC midnight — the phase changes negligibly within a day, but a full moon falling late UTC evening may be 'tomorrow' in your local zone.